Basic phonetic elements of any language are sounds functioning as phonemes. A phoneme is a minimal sound piece helping differ word pairs by their sense:
or grammatical meaning:
In speech phonemes sound in specific variants, allophones. All the phoneme’s variants share some common feature(s). At the same time they all differ in different phonetic environment where they’re conditioned by various positional, combinational and accentual factors.
For example, the [d] phoneme in the word do takes on an outside feature – lip rounding due to the [u:] vowel. In the word dry it becomes alveolar influenced by the alveolar [r] sonant. In the phrase said the man the [d] phoneme loses its apicality and becomes interdental taking an unusual feature from the adjacent [ð] consonant. In the word middle [d] sounds with a plosion articulated by tongue sides. However all these allophones retain the [d] phoneme’s basic characteristic of an occlusive non-sonorous plosive voiced consonant.
Replacing one phoneme with another leads to changing word meaning or distorting its pronunciation. Replacing one allophone with another doesn’t change word meaning though perceived as an accent – dialectal or foreign.
Vowel English sounds are pure musical tone sounds. In pronouncing them the vocal cords are stressed and vibrating. Exhaled air freely goes through the mouth cavity without any obstacles along the way. Air passage is wide with muscular stress spreading across the speech apparatus.
In consonant articulation outgoing air meets a full or partial obstacle. Air flow friction with obstacle sides creates noise principally distinguishing consonants from vowels.
The vocal cords vibrate in articulating voiced consonants and sonants. In pronouncing voiceless consonants they’re passive and absent from articulation. Muscular stress focuses in obstacle location. Consonant noise intensity depends on passage width: the narrower the glottis, the noisier. Voiced consonants in which pronunciation tone prevails over noise are sonants (sonorous) while the rest consonants are non-sonorous.
English sounds include 20 vowels and 24 consonants 7 of which are sonants. There’s great discrepancy between English spelling and pronunciation – 26 alphabetic letters reflect 44 sounds. To show word pronunciation, phonetic transcription is used written in square brackets. One transcription sign stands for one phoneme. Allophones aren’t transcribed.